What value does the change in entropy (ΔS) approach during a process with perfectly ordered substances at absolute zero?

At absolute zero, according to the third law of thermodynamics, the entropy of a perfect crystal approaches zero. This is because, at this temperature, the system is in its lowest energy state, and there is no thermal energy to allow for any disorder or randomness in the arrangement of its particles.

In the case of perfectly ordered substances, there is only one possible microstate for the system, leading to an entropy value of zero. As such, when considering the change in entropy during a process starting from absolute zero for these perfectly ordered substances, the value of ΔS approaches zero, reflecting the absence of disorder in the ordered state at this extreme condition.

Thus, the choice that states this concept accurately addresses the behavior of entropy at absolute zero and is the correct response.